Fatigue Behaviour of Offshore T-Weld Connections Repaired by Grinding and Wet Welding

Abstract

Fixed platforms employed in oil & gas shallow waters industry are subjected to dynamic loads created by winds, waves and currents. However, such loads can produce fatigue damage, like localized cracking in the weld toes of T-welded connections of the submerged structures of fixed platforms. Therefore, to repair localized cracking, a technique that combines grinding and wet welding can be applied at the weld toes of submerged structural connections. Accordingly, in the present work it is presented a methodology to restore the fatigue life of T-welded connections fabricated with A36 plate steel. Consequently, T-welded connections samples were prepared and tested under intact, grinding and grinding-wet-welding repair conditions. For the repair conditions, the weld toes were grinded 6 mm and 10 mm, and wet welding was deposited to fill the grinded material in a hyperbaric chamber, which simulated 50 m, 70 m and 100 m water depths. Afterwards, the repaired connections were subjected to fatigue loads, and the S-N curves were measured for intact and repair conditions. Fatigue results showed that the combined repair technique was able to restore the fatigue life of T-welded connections for a maximum water depth of 50 m. Nonetheless, for water depths of 70 m and 100 m the fatigue life was smaller than for 50 m, but higher compared to the only grinding repair condition.